ADSL (Asymmetric Digital Subscriber Line) is a modem technology that transmits multimedia and high speed data over existing twisted-pair telephones lines concurrently with Plain Old Telephone Service (POTS) signals. VDSL is a higher speed variation of ADSL. The multimedia and high speed data are at a higher frequency than the POTS signals, and components have been developed that can split the higher frequency multimedia and/or data from the lower frequency POTS signal at either end of the transmission path. IDSL is a variation wherein the multimedia and/or high speed data is transmitted concurrently with an ISDN signal instead of the POTS signal. The ISDN, while a higher frequency than the POTS signal, is lower than the multimedia or high speed data signal. Other variations may exist or be developed where signals of differing frequencies are transmitted over existing twisted-pair wiring to a subscriber. The term xDSL will be used herein to generically refer to these different versions of transmitting higher frequency signals (e.g. ADSL, VDSL) over twisted pair concurrently with a relatively lower frequency signal (e.g., POTS, ISDN, or out-of-band signaling used in special services). The terms “first signal” and “second signal” will be used herein to generically refer to at least two different frequency signals transmitted concurrently over twisted-pair wiring and that are intended to be separated, or split, at the subscriber. The term “combined signals” will be used to refer to both the first and second signals combined over a line.
An xDSL architecture connects an xDSL modem on each end of a twisted-pair telephone line, that is, at the “central office” (or node or remote terminal) and at the premises of the subscriber (or customer). The terms “splitting” or “splitter” are used to refer to a circuit or component, for example, a low pass filter or low pass and high pass filter combination, that separates a first signal from a combined signal in the example of a low pass filter and separates both the first and second signals from the combined signal in the example of the low pass and high pass filter combination. Components other than low pass and high pass filters may exist or be developed that also perform this splitting function. The structure and nature of the various splitter circuits or components form no part of the present invention other than the fact that they “split” the combined signal and must be interconnected into an xDSL network in some manner at the customer end of the network.
Splitters have typically been housed with the xDSL modems. However, in view of the requirement for a demarcation point for at least the POTS signal at the network interface device (NID) at the subscriber, some architectural issues arise on how to accommodate the xDSL signal in the existing subscriber interface architecture. U.S. Pat. Nos. 4,488,008; 4,741,032; 5,355,408; and 5,414,765 show various examples of NIDs in use today where POTS modules that have a demarcation point are removably mounted in the NID.
A splitter sold by Alcatel under the designation “A1000 ADSL Remote Splitter” is disclosed as being installed in a NID, however, the Alcatel product suffers from potential drawbacks. First, the installation of the Alcatel splitter requires that the inside wiring be disconnected from the subscriber terminals of one of the POTS modules mounted in the NID and connected to the splitter. Then wires from the splitter are installed to the subscriber terminals on the POTS module. This removal of wiring and rewiring can be a cumbersome process and significantly increases the potential for a wiring mistake on installation. This is especially so considering that POTS modules were designed with a demarcation point that eliminated the need for the subscriber to disconnect any terminal wiring. Secondly, the Alcatel splitter does not provide a separate demarcation point for the POTS-only signal or for the xDSL-only signal. Because the splitter is placed between the demarcation point and the inside wiring, the combined signal passes through the demarcation point (the RJ-11 jack and plug) thereby preventing the ability to have a demarcation point for each isolated signal. Also, the Alcatel splitter takes up four line module spaces in a six line NID. This eliminates its use in NIDs of less than 5 lines or NIDs without four consecutive line module spaces available. Additionally, the Alcatel splitter mounts to an adapter plate that flexes a mounting tang with a projection in the NID as it is snapped into place in the NID by the customer with the telco door closed. Flexing of the mounting tang with the telco door closed is not the intended manner of use of the mounting tang which is meant to flexibly receive POTS modules therein with the telco door open. While insertion is possible while the telco door is closed due to the ramping on the top of the projection on the mounting tang, removal of the adapter plate is not practical without opening the telco door because the tang cannot be readily flexed to clear the projection from the adapter plate. As with the POTS module, ready removal of the adapter plate from the NID requires flexing of the tang that can only be sufficiently flexed when the telco door is open. Because customers do not have the authority to open the telco door, a customer will not be able to practically remove the Alcatel splitter adapter from the NID and may need to place a service call to remove the splitter adapter.
Accordingly, a need exists for an xDSL splitter module for use in the NID that overcomes one or more of the above discussed drawbacks.